Nonconventional mitochondrial ribosomes of malaria parasites Project summary The overall goal of this project is to investigate the structure and function of the mitochondrial ribosome (mitoribosome) in Plasmodium falciparum malaria parasites. The ribosome is a large-molecular-weight complex (~2 MDa) composed of RNAs and proteins that translates genomic information into proteins. Protein translation is a basic and pivotal biological process in all life forms. In malaria parasites, there are evidently three protein translation systems responsible for translating the genomes of the nucleus, the apicoplast and the mitochondrion. The mitoribosome in P. falciparum is phylogenetically and structurally highly divergent relative to the cytosolic and mitochondrial ribosomes of the human host, suggesting the parasite mitoribosome may prove to be an efficacious antimalarial drug target. The research in this proposal will dissect the components and investigate the biological functions of this machinery. Thus, this project would shed light on the structure and function of the ancient protein translational apparatus and expand our knowledge about ribosomal RNA (rRNA) function and protein synthesis in general. Moreover, this study would provide a basis for discovering novel antimalarial inhibitors targeting the mitochondrial protein translation. The mitochondrion of malaria parasites is an essential organelle throughout their complex lifecycle. It is responsible for several critical biosynthetic pathways, such as pyrimidine biosynthesis and iron-sulfur cluster biogenesis, and appears to be essential for energy production through oxidative phosphorylation in insect stages. Maintaining the mitochondrial electron transport chain (mtETC) and the membrane potential is absolutely essential for malaria parasites, and the cytochrome bc1 complex of the mtETC is a proven antimalarial drug target. However, we remain largely ignorant of the structure and function of the parasite mitoribosome, which translates cytochrome b and two subunits of the cytochrome c oxidase. The 6 kb mitochondrial DNA (mtDNA) in malaria parasites is the smallest organellar genome, only encoding three components of the mtETC and ~30 small pieces of fragmented rRNA genes. The discontinuity of the rRNA genes and the complete absence of tRNA genes in the genome have created some doubt regarding the existence of protein translation in this organelle for many years. To address the fundamental questions of malarial mitoribosome, my first aim is to dissect the protein subunits of this machinery through the combination of ribosome isolation and mass spectrometry. The rRNA content in mitoribosome will be characterized by high throughput small RNA-seq. The second aim is to prove that the parasite mitoribosome is functional and essential. Knockout and knock down studies will be carried out on three conserved ribosomal protein subunits. This study will provide information to fill an important scientific gap and offer unique opportunities for future therapeutic interventions.